At a time of persistent unemployment, especially among the less skilled, many wonder whether schools are adequately preparing students for the 21st-century global economy. This is the second study of student achievement in global perspective prepared under the auspices of Harvard's Program on Education Policy and Governance (PEPG). In the 2010 PEPG report, "U.S. Math Performance in Global Perspective," the focus was on the percentage of U.S. public and private school students performing at the advanced level in mathematics. The current study continues this work by reporting the percentage of public and private school students identified as at or above the "proficient" level (a considerably lower standard of performance than the advanced level) in mathematics and reading for the most recent cohort for which data are available, the high-school graduating Class of 2011. Findings reveal that the United States could enjoy a remarkable increment in its annual GDP growth per capita by enhancing the math proficiency of U.S. students. Increasing the percentage of proficient students to the levels attained in Canada and Korea would increase the annual U.S. growth rate by 0.9 percentage points and 1.3 percentage points, respectively. Since long-term average annual growth rates hover between 2 and 3 percentage points, that increment would lift growth rates by between 30 and 50 percent. When translated into dollar terms, these magnitudes become staggering. If one calculates these percentage increases as national income projections over an 80-year period (providing for a 20-year delay before any school reform is completed and the newly proficient students begin their working careers), a back-of-the-envelope calculation suggests gains of nothing less than $75 trillion over the period. That averages out to around a trillion dollars a year. Even if one tweaks these numbers a bit in one direction or another to account for various uncertainties, he reaches the same bottom line: Those who say that student math performance does not matter are clearly wrong. Appended are: (1) Differences in Math Performance of the High School Classes of 2009 and 2011; (2) Performing the Crosswalk; (3) Identifying the Class of 2011; and (4) Critiques of PISA. (Contains 9 figures, 7 tables and 37 footnotes.)